Curable coating composition

ABSTRACT

A curable coating composition is provided which comprises an acrylic resin having an epoxy group and a hydroxyl group in the side chain (A) and a compound having an amino group (B). The composition may further comprise a silane compound having an epoxy group or an amino group in the molecule (C).

TECHNICAL FIELD

[0001] The present invention relates to a curable coating compositionfor the production of a coating having good adhesion to variousmaterials to be coated. More specifically, the present inventionprovides a curable coating composition having good adhesion to hardadhesive metals such as magnesium alloys, aluminum alloys, titaniumalloys and stainless steel and plastics such as polyphenylene sulfide(PPS), polypropylene, acrylonitrile-styrene-butadiene (ABS) resin and analloy of polycarbonate and ABS resin.

BACKGROUND ART

[0002] The functions or properties required for coatings includeadhesion to a material to be coated, protection of the coated materialand good appearance. Various types of coatings have been developed forthese purposes and are put in practical use. Off course, the factor thatinfluences and defines the properties of a coating is a coating resinused in the coating.

[0003] The materials to be coated themselves have been bewilderedlychanged with the progress of times, and recently more complicatedproperties and functions have been required for the materials, such aslight weight, frame retardancy, recycling properties, easybiodegradability and safety, as well as high strength. Under thesecircumstances, as the materials to be coated, the following materialshave been often used: metals having light weight, high strength andabundant resources and easy recycling properties (e.g., magnesiumalloys, aluminum alloys and titanium alloys) as construction materials;plastics having high strength and good transparency (e.g.,polycarbonate) as alternatives to glass; and plastics having good flameretardancy (e.g., Noryl, PPS and PC/ABS resin alloy) for application inhousehold electrical appliances.

[0004] These materials are generally hard adhesive, and particularlythose materials which contains as a constituent a metal atom (e.g., Mg,Al and Zn), such as magnesium alloys, aluminum alloys and titaniumalloys, appear to be hardly adhered with a coating. From the standpointof coatings, these materials are deemed to be hard to adhere, and widelyavailable acrylic melamine resin coatings, acrylic urethane resincoatings, acrylic silicone resin coatings and the like cannot adhere tothe surface of these materials. Therefore, use of primers such asso-called “two-part” epoxy resin coatings are needed.

[0005] Inconveniently, these metals belong to the most non-noble classfrom the viewpoint of electroconductivity. Therefore, there are frequenttroubles such as electric corrosion on the coated material due toimproper application of the coating to the metals, blistering of thecoati film observed in the environmental tests (e.g., water resistancetest), or readily peeling of the coat film.

[0006] To improve and ensure the adhesion of a coating to the materials,it has been widely employed to apply an epoxy resin coating, which isknown to have good adhesive properties, as an under coat (primer).Subsequently, the epoxy resin coating is baked, cured, and coated with atop coating (e.g., acrylic melamine resin coating, polyester resincoating, fluorine resin coating), baked and cured. However, in thistreatment, it is difficult to ensure the sufficient corrosion resistanceof the base material. In practical applications, chemical conversiontreatments has been employed, such as formation of a chromium chromatefilm or a phosphate-chromate film.

[0007] When a chemical conversion film is formed as mentioned above,this coating process can provide a coat film having good properties byvirtue of the outstanding adhesion and corrosion resistance of an epoxyresin. However, the coating process is called “2C2B” (two times ofcoating and two times of baking) or “3C3B” (three times of coating andthree times of baking; often performed when the coating appearance isdisapproval), and the coating workability is quite poor and the yield ofthe coating is low. Moreover, it takes much time for the coatingpretreatment (chemical pre-treatments, such as chemical conversiontreatment with a chromate, etc.) and the coating process, the coatingcost increases, and the efficiency of production of final products isextremely low. Since the epoxy resin forms a tightly cross-linked coatfilm, the adhesion of a re-coating is insufficient.

[0008] The present invention has been made for overcoming theabove-mentioned problems. Accordingly, the object of the presentinvention is to provide a coating having an excellent balance of variousproperties and a good adhesion to hard adhesive materials, in particularhard adhesive metals and plastics such as magnesium alloys, aluminumalloys, PPS and polypropylene, by using a specific acrylic resin as acoating binder.

[0009] Another object of the present invention is to remarkably improvethe corrosion resistance of an electrically less noble metals such asmagnesium alloy and aluminum alloy.

[0010] Still another object of the present invention is to provide acoated article which is coated with the coating, in particular coatedarticle containing, as a constituent element, a magnesium alloy, analuminum alloy, a titanium alloy, PPS, polypropylene, ABS resin, PC/ABSresin alloy and the like.

DISCLOSURE OF INVENTION

[0011] According to the present invention, a curable coating compositionis provided which comprises an acrylic resin having an epoxy group and ahydroxyl group in the side chain (A) and a compound having an aminogroup (B).

BEST MODE FOR CARRYING OUT THE INVENTION

[0012] The coating composition according to the present inventioncomprises, as the film forming components, an acrylic resin having anepoxy group and a hydroxyl group in the side chain (A) and a compoundhaving an amino group (B). The coating composition preferably furthercomprises a silane composition having an epoxy group or an amino groupin the molecule (C).

[0013] The acrylic resin having an epoxy group and a hydroxyl group (A)can be prepared by the radical copolymerization of an acrylic monomerhaving an epoxy group (a-1), an acrylic monomer having a hydroxyl group(a-2) and optionally other unsaturated monomer (a-3). The acrylic resinmay be in the form of blocks, pellets, solution or emulsion-dispersion.

[0014] The acrylic monomer having an epoxy group (a-1) includesacrylates and methacrylates having an epoxy group and an unsaturateddouble bond in the molecule, such as glycidyl acrylate, glycidylmethacrylate, methyl glycidyl acrylate, methyl glycidyl methacrylate and3,4-epoxycyclohexyl methyl acrylate. An acrylic monomer having anon-alicyclic epoxy group (a-1) is preferably used from the view pointof curability, adhesion properties and corrosion resistance. The acrylicmonomer having an epoxy group may be used singly or in combination.

[0015] The acrylic monomer having an epoxy group (a-1) is preferablyused in the copolymerization so that the resulting acrylic resin (A) hasan epoxy equivalent of 200 to 15000, preferably 250 to 8000, morepreferably 450 to 3000. If the epoxy equivalent is less than 200, thenthe curability of the coating may be somewhat degraded, leading to poorchemical resistance and adhesion to the material to be coated. If theepoxy equivalent is larger than 15000, then the storage stability (i.e.,pot-life) of the coating may be too poor, causing poor coatingworkability and poor appearance of the coating.

[0016] The epoxy equivalent can be calculated by the following formula.

Epoxy equivalent=100/[percent copolymerization of acrylic monomer havingepoxy group (a-1)/molecular weight of acrylic monomer having epoxy group(a-1)]

[0017] The acrylic monomer having a hydroxyl group (a-2) includesacrylic compounds having a hydroxyl group and an unsaturated double bondin the molecule, such as 2-hydroxyethyl acrylate, 2-hydroxypropylacrylate, 4-hydroxybutyl acrylate, monoacrylate of cyclohexanedimethanol, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate,4-hydroxybutyl methacrylate, monomethacrylate of cyclohexane dimethanol,polyethylene glycol (meth)acrylate, polypropylene glycol (meth)acrylateand polytetramethylene glycol (meth)acrylate. The acrylic monomer havinga hydroxyl group (a-2) may be used singly or in combination.

[0018] In the present invention, the presence of a hydroxyl group isessential in the acrylic resin (A). If the acrylic resin (A) containsonly an epoxy group, then the adhesion of the coating may be reducedand, therefor, the effects of the invention cannot be achieved. At thesame time, the curing reaction of the coating may not proceedsufficiently, causing poor resistance against water, chemicals andweather.

[0019] The acrylic monomer having a hydroxyl group (a-2) is preferablyused in the copolymerization so that the acrylic resin (A) has ahydroxyl functionality of 3 to 150 mgKOH, preferably 5 to 100 mgKOH,more preferably 10 to 90 mgKOH. If the hydroxyl functionality is lowerthan 3 mgKOH, then the adhesion to a material to be coated may besomewhat degraded. If the hydroxyl functionality is higher than 150mgKOH, then the resistance of the coat film against water, chemicals andso on may be reduced, causing insufficient protection of the material tobe coated (i.e., substrate).

[0020] The hydroxyl functionality can be calculated by the followingformula.

Hydroxyl functionality=561×[percent copolymerization of acrylic monomerhaving hydroxyl group (a-2)/molecular weight of acrylic monomer havinghydroxyl group (a-2)]

[0021] The other unsaturated monomer (a-3) includes, for example, C1-24(fluoro)alkyl esters of (meth)acrylic acid, such as methyl acrylate,ethyl acrylate, butyl acrylate, cyclohexyl acrylate, 2-ethylhexylacrylate, lauryl acrylate, isobornyl acrylate, stearyl acrylate, methylmethacrylate, ethyl methacrylate, butyl methacrylate, cyclohexylmethacrylate, 2-ethylhexyl methacrylate, lauryl methacrylate, isobornylmethacrylate, stearyl methacrylate and trifluoroethyl methacrylate;poly(meth)acrylates of polyalkylene glycols, such as ethylene glycoldiacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate,propylene glycol diacrylate, trimethylolpropane triacrylate,1,4-butanediol diacrylate, ethylene glycol dimethacrylate, diethyleneglycol dimethacrylate, triethylene glycol dimethacrylate, propyleneglycol dimethacrylate, trimethylolpropana trimethacrylate,1,4-butanediol dimethacrylate, polyethylene glycol diacrylate,polyethylene glycol dimethacrylate, polypropylene glycol diacrylate,polypropylene glycol dimethacrylate, polytetramethylene glycoldiacrylate and polytetramethylene glycol dimethacrylate;radical-polymerizable oligomers having at least two acrylic unsaturateddouble bonds in the molecule, such as polyester (meth)acrylate andpolyurethane (meth)acrylate; UV-absorptive unsaturated monomers (R-UVA),such as 2-[2′-hydroxy-5′-(methacryloxymethyl)phenyl]-2H-benztriazol and2-[2′-hydroxy-5′-(methacryloxyethyl)phenyl]-2H-benztriazol; light-stableunsaturated monomers (R-HALS), such as4-acryloyloxy-2,2,6,6-tetramethylpiperidine,4-methacryloyloxy-2,2,6,6-tetramethylpiperidine,4-acryloylamino-2,2,6,6-tetramethylpiperidine and4-methacryloylamino-2,2,6,6-tetramethylpiperidine; unsaturated monomershaving a vinyl group, such as styrene, vinyl acetate and vinyl toluene;and macromonomers having an acrylic unsaturated double bond at thepolymer terminal, such as poly(methyl methacrylate) macromer andpolystyrene macromer. The other unsaturated monomer (a-3) may be usedsingly or in combination.

[0022] Among these monomers, when the acrylic resin (A) is prepared byemulsion copolymerization, poly(meth)acrylates of polyalkylene glycolsare particularly preferably used as the other unsaturated monomer (a-3),such as ethylene glycol diacrylate, diethylene glycol diacrylate,triethylene glycol diacrylate, propylene glycol diacrylate,trimethylolpropane triacrylate, 1,4-butanediol diacrylate, ethyleneglycol dimethacrylate, diethylene glycol dimethacrylate, triethyleneglycol dimethacrylate, propylene glycol dimethacrylate,trimethylolpropane trimethacrylate, 1,4-butanediol dimethacrylate,polyethylene glycol diacrylate, polyethylene glycol dimethacrylate,polypropylene glycol diacrylate, polypropylene glycol dimethacrylate,polytetramethylene glycol diacrylate and polytetramethylene glycoldimethacrylate. When the poly(meth)acrylate of polyalkylene glycol isused in the copolymerization, the coat film tends to be tightlycross-linked, leading to largely improved resistance of the coat filmagainst water, chemicals and weather. More surprisingly, when aparticular poly(meth)acrylate of a polyalkylene glycol, such aspolytetramethylene glycol di(meth)acrylate (number mean molecularweight: 200 to 2000) is used in the copolymerization, good impactresistance and flexibility of the coat film can be provided withoutreduction in hardness, (i.e., mechanical resistance, including scratchresistance).

[0023] The poly(meth)acrylate of polyalkylene glycol is preferablycopolymerized in an amount of 0.01 to 30% by weight, more preferably 0.3to 25% by weight, particularly preferably 0.05 to 20% by weight, basedon the total amount of the monomers constituting the acrylic resin (A).If the amount is less than 0.01% by weight, then satisfactory impactresistance and flexibility of the coat film may be hardly achieved. Ifthe amount is larger than 30% by weight, then the transparency of thecoat film may be somewhat reduced, causing reduction in visualappearance.

[0024] Among these unsaturated monomers, those having a cycloalkylgroup, such as cyclohexyl methacrylate and isobornyl methacrylate, areparticularly suitable, because such monomers can improve the storagestability and weather resistance of the coat film. When such anunsaturated monomer having a cycloalkyl group is contained, the totalcontent is not particularly limited, but is preferably approximately 5to 30% by weight based on the weight of the acrylic resin (A).

[0025] The UV-absorbent unsaturated monomer (R-UVA) is preferred as theother unsaturated monomer (a-3), because not only it can improve theweather resistance of the coat film, but also provide the material to becoated (e.g., polycarbonate) with the protection against degradationcaused by light exposure. The R-UVA is preferably copolymerized in anamount of 0.02 to 40% by weight, more preferably 0.5 to 30% by weight,based on the total amount of the unsaturated monomers constituting theacrylic resin (A). Use of the amount less than 0.5% by weight may notlargely-contribute to the improvement of weather resistance of the coatfilm. Use of the amount larger than 40% by weight may cause undesirablecolor development of the coat film due to the interaction with the aminogroup derived from the compound having an amino group (B) describedbelow and also cause reduction in chemical resistance. Preferredexamples of the R-UVA include2-(2′-hydroxy-5′-methacryloyloxyethylphenyl)-2H-benztriazole and2-(2′-hydroxy-5′-acryloyloxyethylphenyl)-2H-benztriazole.

[0026] The light-stable unsaturated monomer (R-HALS) is preferably usedas the other unsaturated monomer (a-3), because it can improve theweather resistance of the coat film and storage stability of thecoating. Particularly when the R-HALS has a base constant (PKb) of lessthan 8, the same effects as those provided by the below-mentionedcompound having an amino group (B) can be achieved and the curabilityand adhesion to a substrate of the coating can be remarkably improved.The HALS having a base constant of less than 8 includes piperidine-typeHALSs such as 4-acryloyloxy-2,2,6,6-tetramethylpiperidine and4-methacryloyloxy-2,2,6,6-tetramethylpiperidine.

[0027] The R-HALS is preferably copolymerized in an amount of 0.5 to 25%by weight, more preferably 0.5 to 30% by weight, based on the totalamount of the unsaturated monomers constituting the acrylic resin (A).If the amount is less than 0.02% by weight, weather resistance of thecoat film may not be improved remarkably. If of the amount is largerthan 30% by weight, the viscosity of the coating may be increased,resulting in slight reduction in coating workability and adhesionefficiency.

[0028] It is more preferred to copolymerize a macromonomer such aspoly(methyl methacrylate) macromonomer and polystyrene macromonomer.When the macromonomer is copolymerized, the acrylic resin (A) can beformed as a graft copolymer and, therefore, the compatibility with thebelow-mentioned compound having an amino group (B) can be improved,leading to storage stability and curability of the coating andappearance of the coat film. The improvement in compatibility may alsoprovide the improvement in wettability to a substrate and adhesion.

[0029] The macromonomer is preferably copolymerized in an amount of 0.02to 30% by weight, more preferably 0.5 to 20% by weight, based on thetotal amount of the unsaturated monomers constituting the acrylic resin(A). If the amount is less than 0.02% by weight, compatibility may notbe improved satisfactorily, leading to poor curability of the coating.If the amount is larger than 30% by weight, storage stability of thecoating may be reduced to some extent. The number average molecularweight of the macromonomer is not particularly limited, but preferablyabout 1000 to 30000. The macromonomer having the number mean molecularweight of less than 1000 may not exhibit the remarkable effects as agraft copolymer, and leveling properties of the coating and the evennessof the coat film may not be improved remarkably. In contrast, themacromonomer having the number mean molecular weight of larger than30000 may make the coating too viscous, causing slightly poor coatingworkability, and also may make the nature of the resulting graftcopolymer too exaggeratory, causing slightly poor adhesion.

[0030] An example of the production of the acrylic resin (A) is asfollows.

[0031] An acrylic monomer having an epoxy group (a-1), an acrylicmonomer having a hydroxyl group (a-2) and optionally other unsaturatedmonomer (a-3) are subjected to radical copolymerization in apolymerization solvent or disperse medium such as an organic solvent(e.g., toluene, xylene, ethyl acetate, butyl acetate, methyl isobutylketone, butyl cellosolve, isopropyl alcohol) or water, at 20 to 150° C.,thereby producing a acrylic resin (A).

[0032] In the copolymerization, a polymerization initiator, such as anorganic or inorganic azo compound or an organic peroxide, includingα,α-azobisisobutyronitrile, benzoyl peroxide and ammonium persulfate; apolymerization degree modifier such as dodecylmercaptane andalphamethylstyrene dimmer; and non-inonic and/or anionic surfactant(emulsifier), such as poly(sodium oxyethylenealkyl sulfate), may beused.

[0033] The acrylic resin (A) can be produced in the form of solids inthe block polymerization; a slurry or powder or pellets both which areproduced by grinding or pelletization of the slurry in the suspensionpolymerization; a solution in a solvent in the solution polymerizationwith an organic solvent; and an emulsion of polymer particles in waterin an emulsion polymerization with water. Any form of the acrylic resin(A) may be employed depending on the intended use. For use as a coatingas in the case of the present invention, the acrylic resin (A) ispreferably produced by solution polymerization or emulsionpolymerization. This is because the acrylic resin (A) can be used as asolution or emulsion as-is without any purification process such as,separation, precipitation, grinding, pelletization, solvent replacement,re-dissolution in a solvent and distillation.

[0034] In the production by solution polymerization, the acrylic resin(A) preferably has a number average molecular weight of 2000 to 200000,preferably 3000 to 100000. The number average molecular weight of lessthan 2000 may cause reduction in curability of the coating and slightreduction in resistance against chemicals and water. The number averagemolecular weight of higher than 200000, on the contrary, may causeincrease in viscosity of the coating, resulting in poor coating,resulting in poor coating workability. In this case, the pot-life of thecoating may be also shorter, often adversely affecting on storagestability of the coating. However, these are not true for the productionby emulsion polymerization.

[0035] The compound having an amino group (B) can react with the acrylicresin (A) having an epoxy group and an hydroxyl group in the side chain,and serves to provide a cross-link structure to the coat film. At thesame time, as the specific effect of the amino group in the compound(B), the compound (B) can improve the adhesion to a substrate and alsoremarkably improve the corrosion resistance. Any compound having anamino group in the molecule may be used as the compound (B).

[0036] The compound having an amino group (B) includes, for example, acompound having a reactive nitrogen atom, preferably a compound havingan alkylamino, piperidine, piperadine, alkylaminoalkylphenyl,alkylaminoalkylphenol, morpholino, imidazole or imidazoline group, morepreferably a compound having an alkylaminoalkylphenol, imidazole orimidazoline group. The compound having an amino group (B) preferably hasa molecular weight of not larger than 1000. The compound having an aminogroup (B) which has such a molecular weight has a good compatibilitywith the acrylic resin (A) and, therefore the reactivity with theacrylic resin (A) can also be enhanced, leading to improvement incurability and adhesion to a substrate of the coating.

[0037] The compound having an amino group (B) may be an oligomer orpolymer which has an amino group in the backbone, the side chain and/orthe terminal.

[0038] Preferred examples of the compound (B) include those compound(b-1) represented by general formula (I):

[0039] X represents a hydrogen atom, an aliphatic hydrocarbon grouphaving 1 to 10 carbon atoms which has at least one substituent selectedfrom the group consisting of A, B and C, a group having a benzeneskeleton which may substituted by a hydroxyl group and/or an alkyl grouphaving 1 to 10 carbon atoms, or an alicyclic hydrocarbon group having 3to 10 carbon atoms;

[0040] each of A, B and C is independently a group represented bygeneral formula (II) or (III):

[0041] wherein each of R₁, R₂, R₄, R₅, R₆, R₇ and R₈ independentlyrepresents a hydrogen atom or an alkyl group having 1 to 10 carbonatoms; each of R₃ and R₉ independently represents an alkylene grouphaving 1 to 10 carbon atoms or a carbonyl group; and

[0042] each of p, q and r is an integer of 0 or 1, provided that atleast one of p, q and r is 1.

[0043] In the general formula (I), when the total of p, q and r is 1, Xmay be a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, aphenyl group, a hydroxyphenyl group, a hydroxyphenylalkyl group (ofwhich the alkyl group has 1 to 10 carbon atoms) or a cycloalkyl grouphaving 3 to 10 carbon atoms; while when the total of p, q and r is 2 or3, each of these groups (except for hydrogen atom) is substituted by oneor two substituents selected from A, B and C.

[0044] Among those compounds represented by general formula (I), acompound having both an amino group and an hydroxyl group in themolecule is particularly preferred.

[0045] Preferred examples of the compound (B) include (including thosenot represented by general formula (I)) monomethylamine, dimethylamine,trimethylamine, monoethylamine, diethylamine, isopropylamine,di-n-propylamine, diallylamine, diamylamine, di-n-butylamine,diisobutylamine, di-sec-butylamine, N-ethyl-1,2-dimethylpropylamine,N-methylhexylamine, di-n-octylamine, piperidine, 2-pipecoline,3-pipecoline, 4-pipecoline, 2,4-, 2,6-, 3,5-lupetidine,3-piperidinemethanol triethylamine, triethylamine, tributylamine,triallylamine, N-methyldiallylamine, N-methylmorphorine,N,N,N′,N′-tetramethyl-1,2-diaminoethane, N-methylpiperidine, pyridine,4-ethylpyridine, hexamethylenediamine,2,4,6-tris(dimethylaminomethyl)phenol,2,4,6-tris(dimethylaminoethyl)phenol,2,4,6-tris(dimethylaminopropyl)phenol, benzoguanamine, cyanoguanidine,hexamethylenetetramine, polyoxypuropylene-α, ω-diamine,phenyldimethyluea, xylenediamine, lezole polycondensation products,addition products of acrylonitrile-butadiene copolymer and1-(2-aminoethyl)piperadine, N-(2-aminoethyl)piperadine andN,N-dimethylaminopropylamine. These compounds may be used singly or incombination.

[0046] Among these compounds, those compounds having a phenolic hydroxylgroup and an amino group in the molecule, such as2,4,6-tris(dimethylaminomethyl)phenol and2,4,6-tris(dimethylaminoethyl)phenol, are preferred, because they canimprove the hardness and adhesion of the coat film.

[0047] The compound (B) having an amino group may be a compound havingan imidazole group and/or an imidazoline group (b-2). The compoundhaving an imidazole group and/or an imidazoline group (b-2) has goodcompatibility with the acrylic resin (A), can provide a coat film havinga tightly cross-linked structure and having good resistance againstwater and chemicals, and also can improve corrosion resistance ofaluminum alloys and magnesium alloys.

[0048] A polymerization initiator having an imidazole group and/or animidazoline group may be used in the radical copolymerization for theproduction of the acrylic resin (A). In this case, an imidazole groupand/or an imidazoline group that are active can be introduced at theterminal of the acrylic resin (A). As a result, the storage stability ofthe coating can be improved. In addition, dense cross-linking can beformed in the coating and a part of the coating may form an IPN (interpenetrating polymer network) polymer, often leading to dramaticimprovement of mechanical strength and chemical properties of thecoating. The adhesion and corrosion resistance may also be remarkablyimproved.

[0049] The tendencies, effects and functions as mentioned above becomeparticularly noticeable when the acrylic resin (A) is produced byemulsion polymerization.

[0050] The compound having an imidazole group and/or an imidazolinegroup (b-2) includes, for example, 2-methylimidazole,2-undecylimidazole, 2-heptadecylimidazole, 1,2-dimethylimidazole,2-ethyl-4-methylimidazole, 2-phenylimidazole,2-phenyl-4-methylimidazole, 2-methylimidazole, 2-phenylimidazoline,2,2′-azobis[2-(5-methyl-2-imidazolin-2-yl)propane]dihydrochloride(“VA-041”, Wako Pure Chemical Industries, Ltd.),2,2′-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride (“VA-044”, WakoPure Chemical Industries, Ltd.),2,2′-azobis[2-(2-imidazolin-2-yl)propane]disulfate dihydrate (“VA-046B”,Wako Pure Chemical Industries, Ltd.),2,2′-azobis[[1-(2-dihydroxyethyl)-2-imidazolin-2-yl)propane]dihydrochloride(“VA-060”, Wako Pure Chemical Industries, Ltd.),2,2′-azobis[2-imidazolin-2-yl)propane] (“VA-061”, Wako Pure ChemicalIndustries, Ltd.), formylimidazole, diformylimidazole, imidazoldithicarboxylate, imidazole carboxylate, dihydroxymethylimidazole,2-[3-[3-trimethoxysilylpropyloxy]-2-hydroxy-propyl]imidazole,1-(3-trimethoxysilylpropyl)imidazole,1-(3-triethoxysilylpropyl)imidazole,1-acethyl-2-(3-trimethoxysilylpropyl)imidazole and2-(3-trimethoxysilylpropyl)imidazole. The compound having an imidazolegroup and/or an imidazoline group (b-2) may be used singly or incombination.

[0051] The acrylic resin (A) and the compound having an amino group (B)are preferably blended at a ratio of 60/40 to 99.99/0.01 by weight, morepreferably 80/20 to 99.99/0.01 by weight. When the both components areblended at such a ratio, various properties of the coating includingstorage stability, adhesion to a substrate and coat film appearance maybe improved. Surprisingly, in this case, adhesion to a variety ofsubstrates, including plastics (e.g., ABS resin, PPS, PC), inorganicmaterials (e.g., glass, asbestos cement slate, mortar), metals (e.g.,iron, aluminum, magnesium, zinc) and alloys, tends to be largelyimproved. If the blending ratio is less than 60/40 by weight, thehardness of the curability of the coating may be reduced to some extent.If the blending ratio is higher than 99.99/0.01 by weight, on thecontrary, adhesion to various substrates, particularly to metals, may beslightly reduced.

[0052] The coating composition according to the present invention may beproduced by any process, as long as the acrylic resin having an epoxygroup and a hydroxyl group in the side chain (A) and the compound havingan amino group (B) can be dispersed or dissolved to give a homogenoussolution or dispersion. Briefly, for example, the compound having anamino group (B) is added to the acrylic resin (A) while stirring and thestirring is continued until a homogenous solution is produced. In thiscase, it is desirable to previously dissolve or disperse the compoundhaving an amino group (B) in a solvent (e.g., toluene, xylene) so thatthe homogeneity of the solution can be increased and therefore theoperation efficiency can be improved.

[0053] When a polymerization initiator having an imidazole group and/oran imidazoline group (b-3) is used in the preparation of the acrylicresin (A), the homogeneity of the solution is achieved during theemulsion polymerization process. Therefore, any special operation is notrequired.

[0054] If necessary, various coating additives may be blended, such aspigments including titanium oxide, calcium oxide, mica, aluminum andcarbon black; solvents for controlling the viscosity of the coating,including toluene, xylene, ethyl acetate, butyl acetate, methyl alcohol,ethyl alcohol, isopropyl alcohol, n-propyl alcohol, n-butyl alcohol,ethylene glycol monoethyl ether, ethylene glycol monobutyl ether,propylene glycol monomethyl ether, dipropylene glycol n-butyl ether,γ-butyl lactone, methyl isobutyl ketone and water; anti-settling agents;leveling agents; anti-slip agents; defoaming agents; mildew-proofingagents; alga-proofing agents; and anti-corrosive agents. In addition,resins, plasticizers, additives, anti-oxidants, light stabilizers(preferably those of hindered amine types (HALS) having a base constant(PKb) of 8 or higher) and so on which are commonly blended in a coatingmay also be blended.

[0055] Particularly, an anti-oxidant is preferably used, because it canimprove the coloring property of a coating and a coat film.

[0056] Examples of the anti-oxidant include 2,6-di-t-butyl-p-cresol,butylated hydroxyanisole, 2,6-di-t-butyl-4-ethylphenol,stearyl-β-(3,5-di-t-4-hydroxyphenyl) propionate,2,2′-methylenebis(4-methyl-6-t-butylphenol),2,2′-methylenebis(4-ethyl-6-t-butylphenol),4,4′-thiobis(3-methyl-6-t-butylphenol),4,4′-butylidenebis(3-methyl-6-t-butylphenol),3,9-bis(1,1-dimethyl-2-[β-(3-t-butyl-4-hydroxy-5-methylphenyl)propionyloxy]ethyl)2,4,8,10-tetraoxaspyro[5.5]undecane,1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl)butane,1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene,tetrakis-(methylene-3-(3′,5′-di-t-butyl-4′-hydroxyphenyl)propionatemethane, bis[3,3′-bis-(4′-hydroxy-3′-t-butylphenyl)butylic acid] glycolester,1,3,5-tris(3′,5′-di-t-butyl-4′-hydroxybenzyl)-sec-triazine-2,4,6(1H,3H,5H)trione,tocopherol, dilauryl 3,3′-thiodipropionate, dimyristyl3,3′-thiodipropionate, distearyl 3,3′-thiodipropionate, diphenylisodecylphosphate, phenyldiisodecyl-phosphate,4,4′-butylidene-bis(3-methyl-6-t-butylphenylditridecyl) phosphate,cyclic neopentane tetrabis(octadicyl phosphate), tris(nonylphenyl)phosphate, tris(monononylphenyl phosphate), tris(dinonylphenylphosphate), isodecyl pentaerythritol diphosphate,9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide,10-(3,5-di-t-butyl-4-hydroxybenzyl)-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide,10-decyloxy-9,10-9-oxa-10-phosphaphenanthrene,tris(2,4-di-t-buthylphenyl) phosphate, cyclicneopentatetraylbis(2,4-di-t-butylphenyl) phosphate, cyclicneopentatetraylbis(2,6-di-t-butyl-4-methylphenyl) phosphate and2,2-methylenebis(4,6-di-t-butylphenyl) octylphosphate. The antioxidantmay be used singly or in combination.

[0057] Among these compounds, phenol type or phosphate type compoundsare preferably used, such as stearyl-β-(3,5-di-t-butyl-4-hydroxyphenyl)propionate,tetrakis-[methylene-3-(3′,5′-di-t-butyl-4′-hydroxyphenyl)propionate]methane.

[0058] As stated above, the curable coating composition of the presentinvention may comprise the acrylic resin (A) and the compound (B), aswell as various additives. In the curable coating composition, the totalamount of the acrylic resin (A) and the compound (B) is preferably notlower than 50% by weight, more preferably not lower than 80% by weight.

[0059] In the present invention, a silane compound having an epoxy groupor an amino group in the molecule (C) may be blended, so as todramatically improve the adhesion of the coating to various substrates(i.e., materials to be coated), including plastics such as ABS resin, PCresin, Noryl resin, PPS resin, polyamide resin, PC/ABS resin alloy,polyester resin, polystyrene and poly(methyl methacrylate);thermosetting resins such as unsaturated polyester and epoxy resin;inorganic materials such as glass, asbestos cement slate and mortar;metals such as iron, aluminum, magnesium and zinc; and alloys.

[0060] The silane compound having an epoxy group or an amino group inthe molecule (C) is not particularly limited, and includes those silanecompounds represented by general formula (IV) and hydrolysates andcondensates thereof:

[0061] wherein each of R₁₀, R₁₁ and R₁₂ independently represents analkyl group having 1 to 6 carbon atoms or an alkoxy group having 1 to 6carbon atoms; and Y represents an epoxyalkyl group having 1 to 6 carbonatoms, an epoxycycloalkyl group having 4 to 8 carbon atoms, anepoxycycloalkylalkyl group having 5 to 14 carbon atoms or an aminoalkylgroup having 1 to 6 carbon atoms.

[0062] Preferred examples of the silane compound (C) includeγ-glysidoxypropyltrimethoxysilane, γ-glysidoxypropyltriethoxysilane,γ-glysidoxypropylmethyldimethoxysilane,γ-(3,4-epoxycyclohexyl)ethyltriethoxysilane,3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, andhydrolysates and condensates thereof. The compound may be used singly orin combination.

[0063] The silane compound having an epoxy group or an amino group inthe molecule (C) is preferably blended in an amount of 0.02 to 500% byweight, more preferably 0.5 to 300% by weight, based on the total amountof the acrylic resin (A) and the compound (B). If the blending amount isless than 0.02% by weight, the curability of the coating and adhesion toa substrate, particularly to an inorganic substrate or a metal may bereduced. If the blending amount is higher than 500% by weight,wettability of the coating to a substrate may be degraded, causing pooradhesion and coat film appearance.

[0064] According to the present invention, a silane compound having anepoxy group and an alkoxy group in the molecule (c-1) may be blendedwith the acrylic resin (A). In this case, adhesion of the coating to analuminum alloy, a magnesium alloy and so on can be remarkably improved.Moreover, the resistance of the coat film against corrosion, water andsaline water can also be improved without forming a protective film bychemical conversion treatment.

[0065] This notable effect appears to be provided by such a mechanismthat the alkoxysilane group and/or a silanol group in the silanecompound having an epoxy group and a hydrolyzable alkoxysilane group inthe molecule (c-1) can form a tight chemical bond with an aluminum alloy(Al—OH which seems to be present abundantly on the surface of thealloy), a magnesium alloy or the like via orientation to the aluminum ormagnesium alloy or the like or hydrolysis, so that a chemically andelectrically extremely stable, homogenous continuous layer can be formedon the surface of the alloy. In addition, the epoxy group in the silanecompound having an epoxy group and a hydrolyzable alkoxysilane group inthe molecule (c-1) can form a chemical, electrical orcompatibilization-derived tight bond with the functional groups (i.e.,epoxy and hydroxyl groups) of the acrylic resin (A), so that ahomogenous, stiff coat film can be formed on the surface of the alloys.As a result, a good coating appearance can be provided, resistance ofthe coat film against scratch. and weather can be improved, and chemicalor electric development of corrosion on non-iron metals caused by anyexternal factor can be prevented.

[0066] In the present invention, as a coating binder, an acrylicemulsion (A-1) may be used, which is produced by the emulsioncopolymerization of an acrylic monomer having an epoxy group (a-1), anacrylic monomer having an hydroxyl group (a-2) and optionally otherunsaturated monomer (a-3) in an aqueous medium using a reactiveemulsifier having an unsaturated double bond in the molecule (D) and apolymerization initiator having an imidazole group and/or an imidazolinegroup (b-3). Use of the acrylic emulsion (A-1) is desirable, becauseenvironmental pollution caused by organic solvents discharged during theprocess may be prevented.

[0067] The acrylic monomer having an epoxy group (a-1), the acrylicmonomer having a hydroxyl group (a-2) and the other unsaturated monomer(a-3) used may be those mentioned above. As the other unsaturatedmonomer (a-3), a certain poly(meth)acrylate of a polyalkylene glycol ispreferred, such as polytetramethylene glycol di(meth)acrylate (numberaverage molecular weight: 200 to 2000). Use of this type of unsaturatedmonomer (a-3) may provide the coat film with impact resistance andflexibility, without reduction in hardness, accordingly mechanicalstrength (e.g., scratch resistance) of the coat film.

[0068] Recently, the problem of global environmental pollution,including global warming and destruction of the ozone shield, has becomea serious concern. In the filed of coating and painting, strenuousefforts have been made in resolving the problem. For example,development of non-solvent type of coatings (e.g., powder coating,reactive coating), high-solid type of coatings and water-based coatingsfalls under the efforts.

[0069] On the other hand, the functions required for coating includevisual appearance (improvement in surface appearance), protection of amaterial to be coated and so on. However, the current technologies arenot quite satisfactory. For example, in non-solvent type coatings,baking at a higher temperature or irradiation with light is requiredduring film forming process, causing reduction in coating workability.In high-solid type coatings, the molecular weight of a binder should belargely reduced, causing reduction in coat film properties primarilyincluding fundamental properties (e.g., adhesion, water resistance). Forwater-based coatings, unlike lower-humid areas such as Europe, there isan apprehension in steamy areas including Japan that stickiness and poordurability of the coat film may occur.

[0070] Non-iron metals, such as magnesium alloys and aluminum alloys,are generally underwent a chemical conversion treatment (e.g., treatmentwith chromate) due to its poor corrosion resistance. The chemicalconversion treatment such as treatment with chromate, however, may causeserious environmental pollution and ultimately exert serious influenceon biological environment, if the treatment solution is contaminatedinto the waste. Under these circumstances, alternative methods forproviding a anti-corrosive coating have been intensively researched, butany useful method has not yet been found.

[0071] Use of the acrylic emulsion as a binder enables to provide acurable coating composition which is environmentally and ecologicallyfriendly, has good adhesion, corrosion resistance and weatherresistance, can provide a good coating appearance, and suitable as acoating for hard adhesive (non-iron) metals including magnesium alloys,aluminum alloys and stainless steel.

[0072] The emulsion copolymerization for the acrylic emulsion (A-1) isconducted in an aqueous medium. The aqueous medium means a mediumprimarily consisting of water, which may contain hydrophilic organicsolvent that has a solubility to water of 10% or higher at 25° C. in anamount less than 50% by weight, including methyl alcohol, ethyl alcohol,n-propyl alcohol and isopropyl alcohol, if necessary. Water ispreferably ion exchanged water which more preferably has anelectroconductivity of 500 μs/cm or lower.

[0073] The acrylic emulsion (A-1) can be produced by the emulsioncopolymerization of an acrylic monomer having an epoxy group (a-1), anacrylic monomer having an hydroxyl group (a-2) and optionally otherunsaturated monomer (a-3) in an aqueous medium using a reactiveemulsifier having an unsaturated double bond in the molecule (D) and apolymerization initiator having an imidazole group and/or an imidazolinegroup (b-3).

[0074] In the emulsion copolymerization for the acrylic emulsion (A-1),a reactive emulsifier having an unsaturated double bond in the molecule(D) is preferably used. The reactive emulsifier (D) includes, forexample, those compounds represented by formula (V) or (VI). Thereactive emulsifier (D) may be used singly or in combination. Thereactive emulsifier (D) is preferably used in an amount of 0.02 to 30%by weight, preferably 0.02 to 20% by weight, more preferably 0.2 to 18%by weight, particularly preferred 0.5 to 10% by weight, based on thetotal amount of the unsaturated monomers constituting the acrylicemulsion (A). If the reactive emulsifier is used in an amount less than0.02% by weight, aggregation may occur during the emulsionpolymerization. If the reactive emulsifier is used in an amount largerthan 30% by weight, in contrast, water resistance and chemicalresistance may be reduced.

[0075] wherein R represents C₁₈H₃₆F₁; and M represents Na or NH₄.

[0076] wherein R1 represents an alkyl group having 1 to 24 carbon atoms;R2 represents a benzene ring or an alkyl group having 1 to 24 carbonatoms; X represents Na or NH₄; and m is an integer from 5 to 50.

[0077] In formula (V) or (VI), when M or X is Na, the resulting acrylicemulsion (A-1) is retained at pH 5 to 10 and the epoxy group in theacrylic monomer having an epoxy group (a-1) remains in the emulsion,leading to improved curability and adhesion of the coating. Furthermore,when the acrylic emulsion (A-1) is used for coating of a metal with poorcorrosion resistance (e.g., magnesium alloy), a good appearance can beprovided without corrosion of the metal.

[0078] When M or X is NH₄ in the formula (V) or (VI), the resultingacrylic emulsion (A-1) is retained at pH 5 to 10 and the epoxy group inthe acrylic monomer having an epoxy group (a-1) remains in the emulsion,leading to improved curability and adhesion of the coating. In addition,water resistance and humidity resistance can also be remarkablyimproved.

[0079] Examples of the polymerization initiator having an imidazolegroup and/or an imidazoline group (b-3) includes2,2′-azobis(2-(5-methyl-2-imidazolin-2-yl)propane dihydrochloride (WakoPure Chemical Industries, Ltd.; VA-041),2,2′-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride (Wako PureChemical Industries, Ltd.; VA-044),2,2′-azobis[2-(2-imidazolin-2-yl)propane disulfate dihydrate (WakoPure-Chemical Industries, Ltd.; VA-046B),2,2′-azobis[[1-(2-hydroxyethyl)-2-imidazolin-2-yl)propanedihydrochloride (Wako Pure Chemical Industries, Ltd.; VA-060) and2,2′-azobis[2-imidazolin-2-yl)propane] (Wako Pure Chemical Industries,Ltd.; VA-061). The polymerization initiator having an imidazole groupand/or an imidazoline group (b-3) may be used singly or in combination.Among these compounds, those compound having no sulfate ion or chlorineion in the molecule, such as 2,2′-azobis[2-imidazolin-2-yl)propane], areparticularly suitable, because metals such as magnesium alloys andaluminum alloys are not chemically attacked and good coating appearancecan be provided. The polymerization initiator having an imidazole groupand/or an imidazoline group (b-3) serves as a polymerization initiatorin the emulsion copolymerization, and is added to the terminal of thepolymer chain. As a result, a cross-linking reaction occurs betweenpolymers during the curing of the emulsion coating, leading toimprovement in curability and adhesion of the coating.

[0080] The polymerization initiator having an imidazole group and/or animidazoline group (b-3) is desirably used in an amount of 0.001 to 30%by weight, preferably 0.002 to 20% by weight, more preferably 0.005 to10% by weight, based on the total amount of the radical-copolymerizableunsaturated monomers constituting the acrylic emulsion (A-1). Use of thepolymerization initiator having an imidazole group and/or andimidazoline group (b-3) in an amount less than 0.001% by weight is notdesirable, because curability may be insufficient and adhesion andcorrosion resistance of the coating may be poor. Use of the amountlarger than 30% by weight may cause reduction in storage stability ofthe emulsion coating.

[0081] The remarkably important effect of the polymerization initiatorhaving an imidazole group and/or an imidazoline group (b-3) is to keepthe emulsion polymerization system at pH 5 to 10 during the overallprocess of producing the acrylic emulsion (A-1), i.e., until the acrylicresin (A-1) is collected from the emulsion polymerization system. Thiseffect enables to protect the epoxy group present in the acrylicemulsion (A-1) so that the cross-linking properties and curability ofthe coating can be retained or improved. When a silane compound havingan epoxy group and an alkoxysilane group in the molecule (c-1) isblended therein, the epoxy group and alkoxysilane group in the silanecompound (c-1) are also protected, leading to remarkable improvement inadhesion and corrosion resistance.

[0082] In the emulsion polymerization, if other polymerization initiatorsuch as ammonium persulfate or potassium persulfate is used in place ofthe polymerization initiator having an imidazole group and/or animidazoline group (b-3), then the effect of protecting the functionalgroups (i.e., epoxy group, alkoxysilane group) is lost and, as a result,improvement in adhesion, cross-linking properties and corrosionresistance cannot be achieved at all.

[0083] Therefore, it is quite important to use the polymerizationinitiator having an imidazole group and/or an imidazoline group (b-3) inthe emulsion polymerization for producing the acrylic emulsion (A-1).The intended beneficial functions and performance of the acrylicemulsion (A-1) is provided by the use of the polymerization initiatorhaving an imidazole group and/or an imidazoline group (b-3).

[0084] The acrylic emulsion (A-1) desirably has a particle size of 1 to200 nm, preferably 30 to 180 nm, more preferably 40 to 160 nm. Theparticle size of 1 nm or larger is desirable, because the viscosity ofthe emulsion coating can be maintained properly and good coatingworkability can be provided. The particle size of 200 nm or smaller isdesirable, because the emulsion particles are fused one another duringthe drying and curing of the coat film, and good coating appearance,water resistance and chemical resistance can be provided.

[0085] As an example, the acrylic emulsion (A-1) can be produced by theemulsion copolymerization of the acrylic monomer having an epoxy group(a-1), the acrylic monomer having an hydroxyl group (a-2) and optionallyother unsaturated monomer (a-3), in an aqueous medium (e.g., ionexchanged water; preferably having pH of 5 to 7 at 25° C.) at pH 5 to 10at a polymerization temperature of 20 to 100° C., preferably 30 to 80°C., using the polymerization initiator having an imidazole group and/oran imidazoline group and having no sulfate ion or chlorine ion in themolecule (b-3) (e.g., 2,2′-azobis[2-imidazolin-2-yl)propane]), thereactive emulsifier (D) (preferably those which has a ammonium sulfatesalt) and optionally a non-ionic surfactant (e.g., polyoxyethylenenonylphenyl ether). The acrylic monomer having an epoxy group (a-1), theacrylic monomer having an hydroxyl group (a-2) and the other unsaturatedmonomer (a-3) may be any one selected from those compounds as mentionedabove.

[0086] Alternatively, the acrylic emulsion (A-1) can also be produced bythe emulsion copolymerization of the acrylic monomer having an epoxygroup (a-1), the acrylic monomer having an hydroxyl group (a-2) andoptionally other unsaturated monomer (a-3) in an aqueous medium usingthe reactive emulsifier having an unsaturated double bond in themolecule (D) and the polymerization initiator having an imidazole groupand/or an imidazoline group (b-3) in the presence of the silane compoundhaving an epoxy group and an alkoxysilane group in the molecule (c-1).This process is preferred, because various properties of the emulsioncoating, including stability, curability, adhesion, weather resistanceand scratch resistance, can be improved and storage stability can alsobe remarkably improved.

[0087] According to the present invention, it is of course possible tocoat an aluminum or magnesium alloy or the like on which chemicalconversion film (a film of chromium chromate or chromating-phosphating)is provided to improve corrosion resistance and adhesion of the coating.However, the true object of the present invention is to enable thedirect coating of an aluminum or magnesium alloy or the like having nochemical conversion film thereon to provide the same or better effectsand functions as or than those in the substrates with chemicalconversion film.

[0088] The chemical conversion treatment such as treatment with chromatemay cause serious environmental pollution and ultimately exert seriousinfluence on biological environment, if the treatment solution iscontaminated into the waste. Accordingly, it is ideal to perform thecoating without any chemical conversion treatment, particularly withouttreatment with chromate, and those skilled in the art set such a goal.

[0089] According to the present invention, by blending the silanecompound having an epoxy group and an alkoxy group in the molecule (c-1)with the acrylic resin (A), adhesion of the coating to an aluminumalloy, a magnesium alloy and so on can be remarkably improved. Moreover,the resistance of the coat film against corrosion, water and salinewater can also be improved without forming a protective film by chemicalconversion treatment.

[0090] This notable effect appears to be provided by such a mechanismthat the alkoxysilane group and/or a silanol group in the silanecompound having an epoxy group and a hydrolyzable alkoxysilane group inthe molecule (c-1) can form a tight chemical bond with an aluminum alloy(Al—OH which seems to be present abundantly on the surface of thealloy), a magnesium alloy or the like via orientation to the aluminum ormagnesium alloy or the like or hydrolysis, so that a chemically andelectrically extremely stable, homogenous continuous layer can be formedon the surface of the alloy. In addition, the epoxy group in the silanecompound having an epoxy group and a hydrolyzable alkoxysilane group inthe molecule (c-1) can form a chemical, electrical orcompatibilization-derived tight bond with the functional groups (i.e.,epoxy and hydroxyl groups) of the acrylic resin (A), so that ahomogenous, stiff coat film can be formed on the surface of the alloys.As a result, a good coating appearance can be provided, resistance ofthe coat film against scratch and weather can be improved, and chemicalor electric development of corrosion on non-iron metals caused by anyexternal factors can be prevented.

[0091] For making the silane compound having an epoxy group and ahydrolyzable alkoxysilane group in the molecule (c-1) present in theemulsion polymerization system for producing the acrylic emulsion (A-1),it is recommended to dissolve the silane compound (c-1) in theradical-polymerizable unsaturated monomers constituting the acrylicemulsion (A-1) and then subject the mixture to the emulsionpolymerization. In this manner, the silane compound (c-1) can be blendedreadily.

[0092] As stated above, it is important to keep the system at pH 5 to 10during the overall emulsion polymerization. If the pH value is notwithin the range, the epoxy group and the alkoxysilane group are usedfor the reaction and lost during the emulsion polymerization, andtherefore the intended effects cannot be achieved.

[0093] The acrylic emulsion (A-1) may also be produced by the emulsioncopolymerization of the acrylic monomer having an epoxy group (a-1), theacrylic monomer having an hydroxyl group (a-2) and optionally otherunsaturated monomer (a-3) in an aqueous medium using the reactiveemulsifier having an unsaturated double bond in the molecule (D) and thepolymerization initiator having an imidazole group and/or an imidazolinegroup (b-3) in the presence of an acrylic polymer (E) (preferably thebelow-mentioned acrylic polymer (E-1) or (E-2)). This process is alsopreferred, because the rheology of the coating may be controlled readilyand a good appearance without any defects may be obtained. In addition,resistance of the coating against water, chemicals and scratch may alsobe improved.

[0094] The acrylic polymer (E) is preferably blended in the acrylicemulsion (A-1) in an amount of 0.05 to 99% by weight, preferably 0.2 to80% by weight, more preferably 2 to 50% by weight. If the amount is lessthan 0.005% by weight, remarkable improvement may not be achieved. Useof the amount larger than 99% by weight may cause reduction in filmforming properties and therefore a homogenous and even coat film may notbe formed.

[0095] The acrylic polymer (E) desirably has a particle size of 5 to 150nm, preferably 5 to 120 nm, more preferably 10 to 120 nm. If theparticle size is smaller than 5 nm, remarkable improvement may not beachieved. If the particle size is larger than 150 nm, a homogenous andeven coat film may not be formed.

[0096] Examples of the acrylic polymer include those polymers producedby radical copolymerization of a (fluoro)alkyl ester monomer of(meth)acrylic acid, such as methyl methacrylate, n-butyl methacrylate,cyclohexyl methacrylate, lauryl methacrylate, trifluoroethylmethacrylate, methyl acrylate, n-butyl acrylate, cyclohexyl acrylate,lauryl acrylate and trifluoroethyl acrylate; an acrylic monomer havingan epoxy group (a-1); an acrylic monomer having an hydroxyl group (a-2);an unsaturated monomer having a carboxyl group (a-4); and optionallyother unsaturated monomer (a-3). The radical copolymerization may beperformed by any polymerization method, such as solution polymerization,emulsion polymerization, suspension polymerization or blockpolymerization. The acrylic polymer may be in the form of solutionparticles or block. According to the present invention, it is preferredto produce the acrylic polymer as an emulsion by emulsionpolymerization, because handling becomes easy and curability, appearanceand so on of the coating containing the acrylic emulsion (A-1) becomesbetter.

[0097] The acrylic emulsion (A-1) may be produced by the emulsioncopolymerization of the acrylic monomer having an epoxy group (a-1), theacrylic monomer having an hydroxyl group (a-2) and optionally otherunsaturated monomer (a-3) in an aqueous medium using the reactiveemulsifier having an unsaturated double bond in the molecule (D) and thepolymerization initiator having an imidazole group and/or an imidazolinegroup (b-3) in the presence of the acrylic polymer (E) (preferably thebelow-mentioned acrylic polymer (E-1) or (E-2)) and the silane compoundhaving an epoxy group and an alkoxysilane group in the molecule (c-1).This process is also preferred, because the rheology of the coating maybe controlled readily and a good appearance without any defects may beobtained. In addition, curability, adhesion to hard adhesive metals(e.g., aluminum ally, magnesium alloy), and resistance against water,chemical and scratch of the coating may be improved.

[0098] The acrylic polymer (E) is preferably produced by the emulsioncopolymerization of the acrylic monomer having an epoxy group (a-1) andan unsaturated monomer having a carboxyl group (a-4) in an aqueousmedium using the reactive emulsifier having an unsaturated double bondin the molecule (D) and the polymerization initiator having an imidazolegroup and/or an imidazoline group (b-3), provided that the number ofmoles of (a-1)≦the number of moles of (a-4). (Acrylic polymer (E-1))

[0099] As an example, the acrylic polymer (E-1) can be produced by theemulsion copolymerization of the acrylic monomer having an epoxy group(a-1), the unsaturated monomer having an carboxyl group (a-4). andoptionally other unsaturated monomer (a-3), in an aqueous medium (e.g.,ion exchanged water; preferably having an electroconductivity of 500μs/s or lower at 25° C.) at a polymerization temperature of 20 to 100°C. using the polymerization initiator having an imidazole group and/oran imidazoline group and having no sulfate ion or chlorine ion in themolecule (b-3) (e.g., 2,2′-azobis[2-imidazolin-2-yl)propane]) as apolymerization initiator, the reactive emulsifier (D) (preferably thosewhich has a ammonium sulfate salt) and optionally a non-ionic surfactant(e.g., polyoxyethylene nonylphenyl ether). The acrylic polymer (E-1)produced by the emulsion copolymerization desirably has pH of 5.0 to10.0, preferably 6.0 to 9.5, more preferably 6.5 to 8.5, at 25° C. ThepH value of the acrylic polymer (E-1) of 5.0 or higher is preferred,because it becomes readily possible to produce an acrylic emulsion whichcan form a graft polymer with the radical-polymerizable unsaturatedmonomer in the emulsion copolymerization in the subsequent acrylicemulsion production process. The pH value of the acrylic polymer (E-1)of 10.0 or lower is also preferred, because the rate of polymerizationin the subsequent emulsion copolymerization increases sufficiently and,as a result, a problem that a large amount of unreacted monomers remainin the polymerization system is eliminated.

[0100] When the acrylic polymer (E-1) is produced by the emulsionpolymerization in an aqueous medium using the reactive emulsifier havingan unsaturated double bond in the molecule (D) and the polymerizationinitiator having an imidazole group and/or an imidazoline group (b-3),the stability and curability of the coating and corrosion resistance ofthe coated material can be improved.

[0101] When the acrylic polymer (E-1) is produced by the emulsioncopolymerization of the acrylic monomer having an epoxy group (a-1) andan unsaturated monomer having a carboxyl group (a-4) in an aqueousmedium using the reactive emulsifier having an unsaturated double bondin the molecule (D) and the polymerization initiator having an imidazolegroup and/or an imidazoline group (b-3) [provided that the number ofmoles of (a-1)≦the number of moles of (a-4)], in addition to theabove-stated advantages, various properties including resistance of theemulsion coating against solvents, scratch and weather can also beremarkably improved. When the acrylic monomer having an epoxy group(a-1) and the unsaturated monomer having an carboxyl group (a-4) satisfythe relationship: the number of moles of (a-1)≦the number of moles of(a-4), the acrylic polymer (E-1) can form sufficiently cross-linkedpolymer particles and resistance of the acrylic emulsion-containingcoating against water, chemicals and scratch can be improved. Inaddition, the acrylic polymer (E-1) (cross-linked particles) reacts withthe radical-polymerizable unsaturated monomer to form a graft structureduring the emulsion polymerization in the subsequent acrylic emulsionproduction process. As a result, the acrylic polymers which form theacrylic emulsion becomes stable and stiff (i.e., hard to be separated).The scratch resistance, adhesion and weather resistance of the emulsioncoating are also improved.

[0102] The acrylic polymer (E) may be an acrylic polymer (E-2) which isproduced by the emulsion copolymerization of the unsaturated monomercomprising a compound having at least two unsaturated double bond in themolecule [preferably comprising an acrylic monomer having an epoxy group(a-1)] in an aqueous medium using the reactive emulsifier having anunsaturated double bond in the molecule (D) and the polymerizationinitiator having an imidazole group and/or an imidazoline group (b-3).In this case, adhesion of the coating may be improved, and mechanicalproperties (e.g., impact resistance, flexing resistance) may also beremarkably improved.

[0103] Examples of the compound having at least two unsaturated doublebonds in the molecule include unsaturated monomers having at least twoacrylic and/or ethylenical unsaturated double bonds in the molecule,such as ethylene glycol diacrylete, diethylene glycol diacrylate,triethylene glycol diacrylate, polyethylene glycol diacrylate,trimethylolpropana triacrylate, pentaerythritol triacrylate, ethyleneglycol dimethacrylate, diethylene glycol dimethacrylate, triethyleneglycol dimethacrylate, polyethylene glycol dimethacrylate,trimethylolpropana trimethacrylate, pentaerythritol trimethacrylate,ethylene oxide-modified diacrylate of isocyanuric acid, ethyleneoxide-modified triacrylate of isocyanuric acid, ethylene oxide-modifieddimethacrylate of isocyanuric acid, ethylene oxide-modifiedtrimethacrylate of isocyanuric acid, polyurethane diacrylate, polyesterdiacrylate, epoxy diacrylate and divinylbenzene, and oligomers andpolymers thereof. The compound having at least two unsaturated doublebonds in the molecule may be used singly or in combination.

[0104] In the acrylic polymer (E-1), it is preferred that the compoundhaving at least two unsaturated double bonds in the molecule and theacrylic monomer having an epoxy group (a-1) be copolymerized. In thiscase, the acrylic polymer (E-1), together with the acrylic emulsion(A-1), serves to improve the stiffness of the coat film during the filmforming process.

[0105] The acrylic polymer (E-1) is preferably emulsion polymerized atpH 5 to 10. This is because the functional groups in the acrylicemulsion (A-1) can be protected during the production of the acrylicemulsion (A-1), and curability and adhesion of the coating may beimproved.

[0106] The glass transition temperature of the acrylic polymer (E-1) mayvary depending on the intended stiffness, strength and hardness to beprovided to the coat film. The refractive index between the acrylicpolymer (E-1) and the acrylic emulsion (A-1) may be different, dependingon whether a mat (delustered) coat film or a coat film having goodbrightness and clarity is to be formed.

[0107] In addition to the components mentioned above, the coatingcomposition of the present invention may further contain an additivewhich is commonly blended in a coating for the production of a coating,including an organic solvent, such as toluene, xylene, butyl acetate andmethyl isobutyl ketone; a pigment, such as titanium dioxide, calciumcarbonate and carbon black; a pigment dispersing agent; a defoamingagent; an anti-settling agent; and a leveling agent.

[0108] The coating may be applied by any conventional coating method,including spray coating, roll coating and electrostatic coating.

[0109] The material which can be coated with the coating of the presentinvention includes, for example, plastics such asacrylonitrile-styrene-butadiene (ABS) resin, polystyrene (PS) resin,polyphenylene sulfide (PPS) and acrylic resin; metals such as iron,aluminum, magnesium and titanium; alloys; and inorganic constructionmaterials such as mortar and asbestos cement.

EXAMPLES

[0110] The present invention will be described in more detail in thefollowing examples. Unless otherwise stated, all of the numerals denotepart(s) by weight and all of the percentages denote % by weight.

Example 1

[0111] In a 2L four-inlet flask equipped with a stirrer, a thermometerand a nitrogen gas inlet was charged 393.2 g of xylene (XYL)/propyleneglycol monomethyl ether (PM) (=70/30), and heated to 90° C. To a 1Lbeaker were charged 500 g of methyl methacrylate (MMA)/n-butylmethacrylate (BMA)/n-butyl acrylate (BA)/glycidyl methacrylate(GMA)/2-hydroxyethyl methacrylate (HEMA) (=32/20/20/20/8), 1 g ofn-dodecyl mercaptane (DM) and 5 g of α,α-azobisisobutyronitrile (AIBN).The mixture was stirred until a homogenous mixture was produced, therebya monomer mixture was prepared. The monomer mixture was added dropwiseto the flask over 4 hours using a dropping pump (a constant deliverypump). After the dropwise addition was completed, the polymerizationreaction was continued for 1 hour. A mixed slurry of XYL (100 g) andAIBN (0.8 g) was added to the reaction solution dividedly by threeportions at 1-hour intervals. Thereafter, the polymerization wascontinued for additional 1 hour, thereby producing an acrylic resin(A-1), which had a solid content of 50%, an epoxy equivalent of 710, ahydroxyl functionality of 34.5 mgKOH and a number average molecularweight of 22000.

[0112] The acrylic resin (A-1) was blended with 0.5% by weight of2,4,6-tris(dimethylaminomethyl)phenol (TAP), thereby giving a curablecoating composition of Example 1.

[0113] The coating composition was diluted with atoluene/xylene/Anone/butyl acetate/n-butanol (=20/20/20/20/20) mixedsolvent so that the dilution solution had a viscosity of 13 sec. (25°C.) as measured with Ford cup No. 4. In this manner, a test coating (1)which used the curable coating composition of Example 1 was prepared.

Example 2

[0114] In a 2L four-inlet flask equipped with a stirrer, a thermometerand a nitrogen gas inlet were charged 370 g of toluene(TOL)/γ-butyrolactone (=70/30) and 44.5 g of “ARON Macromer AA-6”(methyl methcrylate macromer, 45% solution in toluene; Toagosei Co.,Ltd.) and heated to 90° C. To a 1L beaker were charged 480 g ofMMA/BA/GMA/HEMA [MMA/BA/GMA/HEMA/“ARON Macromer AA-6”=61/5/15/15/4, asdetermined in terms of the solid content of ARON Macromer AA-6] and 5.0g of AIBN. The mixture was stirred until a homogenous mixture wasproduced, thereby a monomer mixture was prepared. The monomer mixturewas added dropwise to the flask over 4 hours using a dropping pump (aconstant delivery pump). After the dropwise addition was completed, thepolymerization reaction was continued for 1 hour. A mixed slurry of TOL(15 g) and AIBN (1.0 g) was added to the reaction solution dividedly bythree portions at 1-hour intervals. Thereafter, the polymerization wascontinued for additional 1 hour, thereby producing an acrylic resin(A-2), which had a solid content of 48%, an epoxy equivalent of 946, ahydroxyl functionality of 64.7 mgKOH and a number average molecularweight of 10000.

[0115] The acrylic resin (A-2) was blended with 5% by weight of“JEFFAMIN EDR-148” (SUN Technochemicals, Inc.), thereby giving a curablecoating composition of Example 2.

[0116] The coating composition was diluted with atoluene/xylene/Anone/butyl acetate/n-butanol (=20/20/20/20/20) mixedsolvent so that the dilution solution had a viscosity of 13 sec. (25°C.) as measured with Ford cup No. 4. In this manner, a test coating (2)which used the curable coating composition of Example 2 was prepared.

Example 3

[0117] The acrylic resin (A-2) was blended with 25% by weight of“SH-6040” (γ-glycidoxypropyl trimethoxysilane; Dow Corning ToraySilicone Co., Ltd.) and 0.25% by weight of “CUREZOL 2E4MZ”, therebyproducing a curable coating composition of Example 3.

[0118] The coating composition was diluted with atoluene/xylene/Anone/butyl acetate/n-butanol (=20/20/20/20/20) mixedsolvent so that the dilution solution had a viscosity of 13 sec. (25°C.) as measured with Ford cup No. 4. In this manner, a test coating (3)which used the curable coating composition of Example 3 was prepared.

Example 4

[0119] The acrylic resin (A-2) was blended with 25% by weight of“SH-6040”, 0.25% by weight of “CUREZOL 2E4MZ” and 5% by weight of“COATAX” MR-409” (an acrylic resin, solid content: 55%, acid value: 53mgKOH, base value: 36 mgKOH, number average molecular weight: 5000;Toray Industries, inc.), thereby producing a curable coating compositionof Example 3.

[0120] The coating composition was diluted with atoluene/xylene/Anone/butyl acetate/n-butanol (=20/20/20/20/20) mixedsolvent so that the dilution solution had a viscosity of 13 sec. (25°C.) as measured with Ford cup No. 4. in this manner, a test coating (4)which used the curable coating composition of Example 4 was prepared.

Example 5

[0121] (i) In a 2L four-inlet flask were charged 574 g of ion exchangedwater (PW) (electroconductivity: 0.5 μs/cm, 25° C.), 35.7 g of “LATEMULS-180A” (a reactive emulsifier corresponding to Compound VI; KaoCorporation), 0.25 g of “VA-061”(2,2′-azobis[2-(2-imidazolin-2-yl)]propane, a polymerization initiatorhaving an imidazoline group; Wako Pure Chemical Industries,. Ltd.) and100 g of MMA/“SIPOMER β-CEA” (β-carboxyethyl acrylate;Rhone-Poulenc)/GMA (MMA/“SIPOMER β-CEA”/GMA=92.5/5.0/2.5) ([GMA] (thenumber of moles of GMA)/[β-CEA] (the number of moles of β-CEA)=1/1.7],and then heated to 70° C. The emulsion polymerization was conducted at70° C. for 2 hours, thereby giving an acrylic polymer (E-1-1).

[0122] (ii) In a dropping vessel 1 were charged 400 g of MMA/BA/“BLEMMERGH” (glycidyl methacrylate (electron grade); NOF Corporation)/HEMA(MMA/BA/GMA/HEMA=55/20/15/10) and 60 g of “SH-6040”. The mixture wasstirred to give a homogenous solution.

[0123] (iii) In a dropping vessel 2 were charged 0.8 g of “VA-061” and80 g of PW. The mixture was stirred to give a homogenous solution.

[0124] (iv) To the acrylic polymer (E-1-1) prepared in step (i) wereadded dropwise the solutions from the dropping vessels 1 and 2 over 2hours. After the addition was completed, the emulsion polymerization wasconducted at 70° C. for additional 2 hours, thereby giving an acrylicemulsion (1) of Example 5.

[0125] The acrylic emulsion (1) had a solid content of 45%, viscosity of250 mPa·s/25° C., pH of 8.2 and particle size of 145 nm.

[0126] The acrylic emulsion (1) was added with 10% by weight of a filmforming auxiliary “DAWANOL DPnB” (dipropylene glycol monobutyl ether;Dow Chemical Japan Limited) and 0.5% by weight of γ-butyrolactone (GBL)PW was added to the mixture so that the solution had a viscosity of 15sec. (25° C.) as measured with Ford cup No. 4. In this manner, anemulsion coating (5) which used the acrylic emulsion (1) of Example 5was prepared.

Example 6

[0127] (i) In a 2L four-inlet flask were charged 292 g of PW(electroconductivity: 0.1 μs/cm, 25° C.), 2.5 g of “ADEKA REASOABSE-1025A” (an ammonium salt ofα-sulfo-ω-(1-nonylphenoxy)methyl-2-(2-puropenyloxy)ethoxy-poly(oxy-1,2-ethanediyl;a reactive emulsifier corresponding to formula (VI); Asahi Denka KogyoKK) and then stirred.

[0128] In 50 g of BA/“BLEMMER GH”/trimethylolpropane triacrylate (TMPTA)(=94/5/1) was dissolved 1 g of “SANOL LS-2626”(1-[2-[3-(3,5-di-t-butyl-4-hydroxyphenyl)propyonyloxy]ethyl]-4-[3-(3,5-di-t-butyl-4-hydroxyphenyl)propyonyloxy]-2,2,6,6-tetramethylpiperidine;HALS with pKb=12; Sankyo Co., Ltd.) to give a monomer solution.

[0129] In a homogenizer were charged 50 g of PW (25° C.), 5.5 g of“ADEKA REASOAB SE-1025A”, 0.1 g of “VA-061” and all of the monomersolution. The mixture was emulsified at 5000 rpm for 10 min. at 25° C.to give a monomer emulsion (1).

[0130] All of the monomer emulsion (1) was charged in a flask and thensubjected to emulsion polymerization at 70° C. for 150 min. to producean acrylic polymer (E-2-1), which had particle size of 50 nm and pH of7.3.

[0131] (ii) In 450 g of MMA/BMA/BA/“BLEMMER GH”/HEMA/“BLEMMER PDT-650”(polytetramethylene glycol dimethacrylate; NOF Corporation)(=55/5/10/15/10/5) was dissolved 9 g of “SANOL LS-2626”. The solutionwas added with 50 g of “SH-6040” to give a homogenous solution.

[0132] In a homogenizer were charged 450 g of PW (25° C.) and 2.5 g of“VA-061”. The solution was stirred to dissolve the “VA-061”. To thesolution were added all of the above-prepared solution, 37 g of “ADEKAREASOAB SE-1025A” and 2.0 g of “EMULGEN 1135S-70” (a nonionicsurfactant; Kao Corporation). The mixed solution was emulsified at 5000rpm for 10 min. at 25° C. to give a monomer emulsion (2).

[0133] The monomer emulsion (2) was added dropwise to a flask over 3hours. After the addition was completed, the reaction solution wassubjected to emulsion polymerization at 70° C., for 2 hours and thenaging reaction to produce an acrylic emulsion (A-2).

[0134] The acrylic emulsion (A-2) had a solid content of 40%, viscosityof 600 mPa·s, particle size of 98 nm and pH of 7.2.

[0135] The acrylic emulsion (A-2) was blended with 2% by weight of“Surfynol 104” (2,4,7,9-tetramethyl-5-decyne-4,7-diol; a surfactant(defoaming agent); Air Products & Chemicals) (which was previouslydissolved at 65° C.) and 10% by weight of a film forming agent “DAWANOLTPnB” (tripropylene glycol mono-n-butyl ether: Dow Chemical JapanLimited). PW was added to the mixture so that the solution had aviscosity of 15 sec. (25° C.) as measured with Ford cup No. 4. In thismanner, an emulsion coating (6) for use in the coating test wasprepared.

Example 7

[0136] (i) In a stainless steel vessel were charged 796 g of PW(electroconductivity: 0.1 μs/cm, 25° C.) and 4.0 g of “VA-061” and thenstirred to give a homogenous aqueous initiator solution.

[0137] (ii) In a 5L four-inlet flask was charged 808 g PW and 128 g of“ADEKA REASOAB SE-1025A” and then stirred.

[0138] (iii) In a stainless steel vessel was charged 160 g ofBA/“BLEMMER GH”/TMPTA/“SANOL LS-2626” (=92.5/5.0/0.5/2.0) and thenstirred to give a homogenous monomer solution (1).

[0139] (iv) The monomer solution (1) was charged in a flask and thenstirred. The heating of the solution was started. When the temperatureof the solution reached 60° C., a portion (20%) of the aqueous initiatorsolution was added to the solution, and then the heating was continueduntil the temperature reached 68° C. At this point of time, emulsionpolymerization was conducted at 68° C. for 150 min. to produce anacrylic polymer (E-2-2), which had particle size of 30 nm and pH of 7.1.

[0140] (v) In a stainless steel vessel was charged 1440 g ofMMA/BA/HEMA/“BLEMMER GH”/“SH-6040”/“BLEMMER PDT-650”/“SANOL LS-2626”(=41.9/12.6/11.1/16.7/8.9/6.7/2.1) and then stirred to give a homogenousmonomer solution (2).

[0141] (vi) In an emulsifier apparatus were charged 720 g of PW and 64 gof “ADEKA REASOAB SE-1025A” and then charged the monomer solution (2).The mixture was emulsified at 5000 rpm for 10 min. at 25° C. to give amonomer emulsion (1).

[0142] (vii) The monomer emulsion (1) and the remainder (i.e. 80%) ofthe aqueous initiator solution were added dropwise to a flask over 4hours and 5 hours, respectively, while keeping the polymerizationtemperature at 68° C.

[0143] (viii) After the addition was completed, aging reaction wasconducted for additional 1 hour at 68° C. to produce an acrylic emulsion(A-3).

[0144] The acrylic emulsion (A-3) had a solid content of 40%, viscosityof 800 mPa·s, particle size of 92 nm and pH of 7.2.

[0145] The acrylic emulsion (A-3) was blended with 2% by weight of“Surfynol 104” (which was previously dissolved at 65° C.) and 10% byweight of “DAWANOL TPnB” as a film forming agent. PW was added to themixture so that the solution had a viscosity of 15 sec. (25° C.) asmeasured with Ford cup No. 4. In this manner, an emulsion coating (7-1)for use in the coating test was prepared.

[0146] The acrylic emulsion (A-3) was blended with 2% by weight of“Surfynol 104” (which was previously dissolved at 65° C.) and 10% byweight of “DAWANOL TPnB” as a film forming agent. PW was added to themixture so that the solution had a viscosity of 50 sec. (25° C.) asmeasured with Ford cup No. 4. In this manner, an emulsion coating (7-2)for use in the coating test was prepared.

Example 8

[0147] (i) In a stainless steel vessel were charged 796 g of PW(electroconductivity: 0.1 μs/cm, 25° C.) and 4.0 g of “VA-061” and thenstirred to give a homogenous aqueous initiator solution.

[0148] (ii) In a 5L four-inlet flask was charged 808 g of PW and 128 gof “ADEKA REASOAB SE-1025A” and then stirred.

[0149] (iii) In a stainless steel vessel was charged 160 g ofMMA/“BLEMMER GH”/TMPTA/“SANOL LS-2626” (=92.5/5.0/0.5/2.0) and thenstirred to give a homogenous monomer solution (1).

[0150] (iv) The monomer solution (1) was charged in a flask and thenstirred. The heating of the solution was started. When the temperatureof the solution reached 60° C., a portion (20%) of the aqueous initiatorsolution was added to the solution, and then the heating was continueduntil the temperature reached 68° C. At this point of time, emulsionpolymerization was conducted at 68° C. for 150 min. to produce anacrylic polymer (E-2-3), which had particle size of 25 nm and pH of 7.2.

[0151] (v) In a stainless steel vessel was charged 1440 g ofMMA/BA/HEMA/“BLEMMER GH”/“SH-6040”/“BLEMMER PDT-650”/“SANOL LS-2626”(=46.6/12.6/11.1/16.7/8.9/2.0/2.1) and then stirred to give a homogenousmonomer solution (2).

[0152] (vi) In an emulsifier apparatus were charged 720 g of PW and 64 gof “ADEKA REASOAB SE-1025A” and then charged the monomer solution (2).The mixture was emulsified at 5000 rpm for 10 min. at 25° C. to give amonomer emulsion (2).

[0153] (vii) The monomer emulsion (2) and the remainder (i.e. 80%) ofthe aqueous initiator solution were added dropwise to a flask over 4hours and 5 hours, respectively, while keeping the polymerizationtemperature at 68° C.

[0154] (viii) After the addition was completed, aging reaction wasconducted for additional 1 hour at 68° C. to produce an acrylic emulsion(A-4).

[0155] The acrylic emulsion (A-4) had a solid content of 40%, viscosityof 1200 mPa·s, particle size of 88 nm and pH of 7.2.

[0156] The acrylic emulsion (A-4) was blended with 2% by weight of“Surfynol 104” (which was previously dissolved at 65° C.) and 10% byweight of “DAWANOL TPnB” as a film forming agent. PW was added to themixture so that the solution had a viscosity of 15 sec. (25° C.) asmeasured with Ford cup No. 4. In this manner, an emulsion coating (8-1)for use in the coating test was prepared.

[0157] The acrylic emulsion (A-4) was blended with 2% by weight of“Surfynol 104” (which was previously dissolved at 65° C.) and 10% byweight of “DAWANOL TPnB” as a film forming agent. PW was added to themixture so that the solution had a viscosity of 50 sec. (25° C.) asmeasured with Ford cup No. 4. In this manner, an emulsion coating (8-2)for use in the coating test was prepared.

Example 9

[0158] (i) In a 2L four-inlet flask were charged 800 g of PW(electroconductivity: 1.0 μs/cm, 25° C.), 35.7 g of “LATEMUL S-180” (areactive emulsifier corresponding to formula (V); Kao Corporation), 0.25g of “VA-061” and 50 g of MMA/BA/GMA/HEMA (=65/10/15/10), and thenheated to 80° C.

[0159] The emulsion polymerization was conducted at 80° C. for 30 min.

[0160] (ii) In a dropping vessel 1 were charged 450 g of MMA/BA/GMA/HEMA(=65/10/15/10) and 75 g of “SH-6040”. The mixture was stirred to give ahomogenous solution.

[0161] (iii) In a dropping vessel 2 were charged 1.0 g of “VA-061” and100 g of PW. The mixture was stirred to give a homogenous solution. (iv)The solutions in the dropping vessels 1 and 2 were added dropwise to aflask over 3 hours. After the addition was completed, the emulsionpolymerization was conducted at 80° C. for additional 2 hours, therebygiving an acrylic emulsion (A-5) of Example 9.

[0162] The acrylic emulsion (A-5) had a solid content of 40%, viscosityof 120 mPa·s and pH of 8.0, and contained no sulfate ion.

[0163] The acrylic emulsion (A-5) was added with 15% by weight ofγ-butyrolactone (GBL) as a film forming auxiliary. PW was added to themixture so that the solution had a viscosity of 15 sec. (25° C.) asmeasured with Ford cup No. 4. In this manner, a test emulsion coating(9) was prepared.

Comparative Example 1

[0164] Substantially the same procedure as in Example 3 was conducted,except that the monomer composition for the acrylic resin (A-2) waschanged to MMA/BA/GMA/“ARON Macromer AA-6” (=61/20/15/4, as determinedin terms of the solid content of ARON Macromer AA-6), thereby giving acurable coating composition of Comparative Example 1.

[0165] The coating composition was diluted with atoluene/xylene/Anone/butyl acetate/n-butanol (=20/20/20/20/20) mixedsolvent so that the dilution solution had a viscosity of 13 sec. (25°C.) as measured with Ford cup No. 4. In this manner, a test coating (10)which used the curable coating composition of Comparative Example 1wasprepared.

Comparative Example 2

[0166] (i) In a 2L four-inlet flask were charged 800 g of PW, 35.7 g of“LATEMUL-S-180”, 0.25 g of ammonium persulfate and 50 g ofMMA/BA/GMA/HEMA (=65/10/15/10), and then heated to 80° C.

[0167] The emulsion polymerization was conducted at 80° C. for 30 min.

[0168] (ii) In a dropping vessel 1 were charged 450 g of MMA/BA/GMA/HEMA(=65/10/15/10) and 75 g of “SH-6040”. The mixture was stirred to give ahomogenous solution.

[0169] (iii) In a dropping vessel 2 were charged 1.0 g of ammoniumpersulfate and 100 g of PW. The mixture was stirred to give a homogenoussolution.

[0170] (iv) The solutions in the dropping vessels 1 and 2 were addeddropwise to a flask over 3 hours. After the addition was completed, theemulsion polymerization was conducted at 80° C. for additional 2 hours,thereby giving an acrylic emulsion (A-6) of Comparative Example 2.

[0171] The acrylic emulsion (A-6) had a solid content of 40%, viscosityof 180 mPa·s and pH of 3.8.

[0172] The acrylic emulsion (A-6) was neutralized with aqueous ammoniumto pH 8.0, and then added with 15% by weight of GBL as a film formingauxiliary. PW was added to the mixture so that the solution had aviscosity of 15 sec. (25° C.) as measured with Ford cup No. 4. In thismanner, a comparative emulsion coating (11) was prepared.

Comparative Example 3

[0173] Substantially the same procedure as in Example 6 was conducted,except that ammonium persulfate was used in place of “VA-061”, therebygiving an acrylic emulsion (A-7) of Comparative Example 3.

[0174] The acrylic emulsion (A-7) had a solid content of 40%, viscosityof 500 mPa·s and pH of 4.2.

[0175] The acrylic emulsion (A-7) was neutralized with aqueous ammoniumto pH 8.0, and then added with 10% by weight of “DAWANOL DPnB” as a filmforming auxiliary. PW was added to the mixture so that the solution hada viscosity of 15 sec. (25° C.) as measured with Ford cup No. 4. In thismanner, a comparative emulsion coating (12) was prepared.

[0176] The coatings (1) to (12) prepared in Example 1 to ComparativeExample 3 were used to assess the performance and properties of coatfilms. The test methods and results are as follows.

[0177] Test 1

[0178] [Preparation of Test Coated Plates]

[0179] The coatings (1), (2), (4) and (10) were used to prepare coatedplates to be tested.

[0180] [Preparation of Coated Plates for Adhesion and Water ResistanceTests]

[0181] (1) Each coating was spray coated onto a PPS plate to the coatingthickness of 30 μm, and then baked at 120° C. for 30 min. The coatedplate was allowed to dry at room temperature for 3 days, which was usedin the following adhesion test.

[0182] (2) An AZ91D magnesium alloy plate (thickness: 2 mm), which hadbeen tixo-molded, was barreled, defatted with aqueous 0.5% NaOHsolution, subjected to conversion treatment with chromate in aconventional manner, spray coated with each coating to the coatingthickness of 15 μm, and then baked at 160° C. for 20 min. The coatedplate was allowed to dry at room temperature for 3 days, which was usedin the following adhesion and water resistance tests to be tested

[0183] The methods for tests and evaluations were as follows. Theresults are shown in Table 1.

[0184] 1. Adhesion

[0185] The test was conducted according to JIS K 5400 (the cross-cuttest). A coat film of which the test result was 100/100 was determined“success”.

[0186] 2. Water Resistance

[0187] A test coated plate was immersed in ion exchanged water (50° C.)for 48 hours and then allowed to dry at room temperature for 1 day. Theplate was determined for its appearance and then subjected to theadhesion test. A coat film of which appearance had no change (e.g.,blister, blushing (whitening)) was determined “success”. In the colordevelopment test of a coat film, ΔE was determined with CR-331 (MinoltaCo., Ltd.), and a coat film having a ΔE value of 2 or lower wasdetermined “success”. In the adhesion (i.e., the test for re-adhesionafter water-immersing and drying) test, a coat film of which the testresult was 100/100 was determined “success”. TABLE 1 Test results forcoat film Coating Coating Coating Coating 1 2 4 10 Test items (Ex. 1)(Ex. 2) (Ex. 4) (CEx. 1) PPS plate Adhesion 100/100 100/100 100/10040/100 Water resistance Appearance Success Success Success Success Colordevelopment Success Success Success Blushing Adhesion Success SuccessSuccess  0/100 AZ91D plate Adhesion 100/100 100/100 100/100  0/100 Waterresistance Appearance Success Success Success Success Color developmentSuccess Success Success Blister Adhesion Success Success Success  0/100

[0188] Test 2:

[0189] [Preparation of Test Coated Plates]

[0190] The coatings (2), (4) and (10) were used for the various tests.The methods for tests and evaluation are as follows. The results areshown in Table 2.

[0191] [Preparation of Test Coated Plates]

[0192] An AZ31 magnesium alloy plate (thickness: 1 mm), which had beenmolded by press forging, was subjected to hair-line processing, defattedwith aqueous 0.5% NaOH solution, splay coated with each of the coatings(3), (4) and (10) to the coating thickness of 15 μm, and then baked at160° C. for 20 min.

[0193] [Evaluation Methods]

[0194] [Coat Film Appearance]

[0195] The appearance of a coat film after baking was visuallyevaluated. A coat film of which surface was even and had no cratering,cracking or flashing was determined “success (good)”.

[0196] [Adhesion]

[0197] Adhesion of a test coat film was evaluated by the cross-cut testaccording to JIS K 5400. A coat film of which the test result was100/100 was determined “success”, while a coat film of which the testresult was not so was determined “failed”.

[0198] [Coat Film Hardness]

[0199] Harness of a coat film was determined as the scratch resistanceby the pencil harness test according JIS K 5400. A coat film having aharness of 2H or higher was determined “success”.

[0200] [Water Resistance]

[0201] A coated plate was immersed in hot water (50° C.) for 10 days andthen evaluated for the appearance of the coat film. A coat film of whichsurface had no flashing, blister, blushing or peeling was determined“success (good)”.

[0202] [Salt Spray Test]

[0203] The test was conducted according to JIS K 5400 using a salt spraytester for 100 hours. A coated plate of which the cut area had nocorrosion and of which the film surface had no blister, peeling ordiscoloration was determined “success (no problem)”. TABLE 2 Coat filmtest results Coating 3 Coating 4 Coating 10 Test items (Ex. 3) (Ex. 4)(CEx. 1) Coat film appearance Success Success Success Adhesion 100/100100/100 0/100 Coat film hardness 5 H 3 H F Water resistance SuccessSuccess Salt spray property Appearance Success Success Corrosion in thewhole area Adhesion 100/100 100/100 0/100

[0204] Test 3:

[0205] The coatings (5), (6), (7-1), (8-1), (9), (11) and (12) were usedfor the various tests. The methods for tests and evaluation are asfollows. The results are shown in Table 3.

[0206] [Preparation of Test Coated Plates]

[0207] Each of aluminum plates JIS A-1100, 3004 and 5052 (thickness: 1mm) was defatted with aqueous 3% solution of “Fine Cleaner 315” (adefatting agent; Nihon Perkerizing Co., Ltd.) at 60° C. for 5 min.,washed with water, dried with air, spray coated with each of thecoatings to the film thickness of 20 μm, and then baked at 230° C. for 1min.

[0208] [Evaluation Methods for Coat Films]

[0209] [Coat Film Appearance]

[0210] The appearance of a coat film after baking was visuallyevaluated. A coat film of which surface was even and had no cratering,cracking or flashing was determined “success (good)”.

[0211] [Adhesion]

[0212] Adhesion of a coat film was evaluated by the cross-cut testaccording to JIS K 5400. A coat film of which the test result was100/100 was determined “success”, while a coat film of which the testresult was not so was determined “failed”.

[0213] [Coat Film Hardness]

[0214] Harness of a coat film was determined as the scratch resistanceby the pencil harness test according JIS K 5400. A coat film having aharness of F or higher was determined “success”.

[0215] [Water Resistance]

[0216] A coated plate was immersed in hot water (50° C.) for 10 days andthen evaluated for the appearance of the coat film. A coat film of whichsurface had no flashing, blister, blushing or peeling was determined“success (good)”.

[0217] [Humidity Resistance]

[0218] A coated plate was exposed to a 98% RH atmosphere for 1000 hours,and then evaluated for the appearance. A coat film of which surface hadno flashing, blister, blushing or peeling was determined “success(good)”.

[0219] [Salt Spray Test]

[0220] The test was conducted according to JIS K 5400 using a salt spraytester for 1000 hours. A coated plate of which the cut area had nocorrosion and of which the film surface had no blister, peeling ordiscoloration was determined “success (no problem)”.

[0221] Test 4:

[0222] The coatings (7-2) and (8-2) were used and tested for coatingworkability on a roll coater. The coating was conducted by the methodcommonly employed for coil coating of an aluminum alloy and an ironplate.

[0223] Both of the coatings (7-2) and (8-2) exhibited good pickupproperty, application property, coat film thickness controlling property(1 to 30 μm) and coat film appearance. TABLE 3 Coat film test resultsCoating Coating Coating Coating Coating Coating Coating 5 6 7-1 8-1 9 1112 Test items (Ex. 5) (Ex. 6) (Ex. 7) (Ex. 8) (Ex. 9) (CEx. 2) (CEx. 3)Coat film appearance 1100 Success Success Success Success SuccessCissing Success 3004 Success Success Success Success Success CissingSuccess 5052 Success Success Success Success Success Success SuccessAdhesion 1100 100/100 100/100 100/100 100/100 100/100 20/100 20/100 3004100/100 100/100 100/100 100/100 100/100 20/100 20/100 5052 100/100100/100 100/100 100/100 100/100 20/100 20/100 Coat film hardness 1100 2H H H 3 H 2 H F H 3004 2 H H H 3 H 2 H H H 5052 2 H 2 H 2 H 4 H 3 H H 2H Water resistance 1100 Success Success Success Success SuccessBlushing, Blushing, peeling peeling/ 3004 Success Success SuccessSuccess Success Blushing, Blushing, peeling peeling 5052 Success SuccessSuccess Success Success Blushing, Blushing, peeling peeling Humidityresistance 1100 Success Success Success Success Success Blushing,Blushing, peeling peeling/ 3004 Success Success Success Success SuccessBlushing, Blushing, peeling peeling 5052 Success Success Success SuccessSuccess Blushing, Blushing, peeling peeling Salt spray test 1100 SuccessSuccess Success Success Success Corrosion in Corrosion in the whole areathe whole area 3004 Success Success Success Success Success Corrosion inCorrosion in the whole area the whole ares 5052 Success Success SuccessSuccess Success Corrosion in Corrosion in the whole area the whole area

[0224] Industrial Applicability

[0225] A curable coating composition can be provided which has goodadhesion to hard adhesive metals such as magnesium alloys, aluminumalloys titanium alloys and stainless steel and plastics such aspolystyrene, acrylonitrile-styrene-butadiene (ABS) resin andpolypropylene.

1. A curable coating composition comprising an acrylic resin having anepoxy group and a hydroxyl group in the side chain (A) and a compoundhaving an amino group (B).
 2. A curable coating composition comprisingan acrylic resin having an epoxy group and a hydroxyl group in the sidechain (A), a compound having an amino group (B) and a silane compoundhaving an epoxy group or an amino group in the molecule (C), the silanecompound (C) being contained in an amount of from 0.02 to 500% by weightbased on the total amount of the acrylic resin (A) and the compoundhaving an amino group (B).
 3. The curable coating composition accordingto claim 1 or 2, wherein the compound having an amino group (B) has amolecular weight of not greater than
 1000. 4. The curable coatingcomposition according to claim 1 or 2, wherein the acrylic resin (A) andthe compound having an amino group (B) are present at a ratio of from60/40 to 99.99/0.01 by weight.
 5. The curable coating compositionaccording to claim 1 or 2, wherein the acrylic resin (A) is prepared bypolymerizing monomers comprising an acrylic monomer having an epoxygroup (a-1) and an acrylic monomer having an hydroxyl group (a-2). 6.The curable coating composition according to claim 1 or 2, wherein thecompound having an amino group (B) is represented by general formula (I)(b-1):

wherein: X represents a hydrogen atom, an aliphatic hydrocarbon grouphaving 1 to 10 carbon atoms which has at least one substituent selectedfrom the group consisting of A, B and C, a group having a benzeneskeleton which may substituted by a hydroxyl group and/or an alkyl grouphaving 1 to 10 carbon atoms, or an alicyclic hydrocarbon group having 3to 10 carbon atoms; each of A, B and C is independently a grouprepresented by general formula (II) or (III):

wherein each of R₁, R₂, R₄, R₅, R₆, R₇ and R₈ independently represents ahydrogen atom or an alkyl group having 1 to 10 carbon atoms; each of R₃and R₉ independently represents an alkylene group having 1 to 10 carbonatoms or a carbonyl group; and each of p, q and r is an integer of 0 or1, provided that at least one of p, q and r is
 1. 7. The curable coatingcomposition according to claim 1 or 2, wherein the compound having anamino group (B) is a compound having an imidazole group and/or animidazoline group (b-2).
 8. The curable coating composition according toclaim 1 or 2, wherein the acrylic resin (A) is prepared by thepolymerization using a polymerization initiator having an imidazolegroup and/or an imidazoline group (b-3)
 9. An acrylic emulsion producedby the emulsion copolymerization of monomers comprising an acrylicmonomer having an epoxy group (a-1) and an acrylic monomer having anhydroxyl group (a-2) using a reactive emulsifier having an unsaturateddouble bond in the molecule (D) and a polymerization initiator having animidazole group and/or an imidazoline group (b-3).
 10. An acrylicemulsion produced by the emulsion copolymerization of monomerscomprising an acrylic monomer having an epoxy group (a-1) and an acrylicmonomer having an hydroxyl group (a-2) using a reactive emulsifierhaving an unsaturated double bond in the molecule (D) and apolymerization initiator having an imidazole group and/or an imidazolinegroup (b-3) in the presence of a silane compound having an epoxy groupand an alkoxysilane group in the molecule (c-1).
 11. The acrylicemulsion according to claim 9 or 10, wherein the acrylic emulsion isproduced by the emulsion copolymerization under the condition of pH 5 to10.
 12. The acrylic emulsion according to claim 9 or 10, wherein theacrylic emulsion is produced by the emulsion copolymerization in anaqueous medium in the presence of an acrylic polymer (E).
 13. Theacrylic emulsion according to claim 12, wherein the acrylic polymer (E)is produced by the emulsion copolymerization of at least two unsaturatedmonomers comprising an unsaturated monomer having at least an epoxygroup (a-1) and an unsaturated monomer having a carboxyl group (a-4) inan aqueous medium using a reactive emulsifier having an unsaturateddouble bond in the molecule (D) and a polymerization initiator having animidazole group and/or an imidazoline group (b-3), the number of molesof (a-1) is equal or smaller than that of (a-4).
 14. The acrylicemulsion according to claim 12, wherein the acrylic polymer (E) isproduced by the emulsion copolymerization of an unsaturated monomercomprising a compound having at least two unsaturated double bonds inthe molecule in an aqueous medium using a reactive emulsifier having anunsaturated double bond in the molecule (D) and a polymerizationinitiator having an imidazole group and/or an imidazoline group (b-3).15. A magnesium alloy having thereon a coat film formed with a curablecoating composition as claimed in claim 1 or
 2. 16. A magnesium alloyhaving thereon a coat film formed with a curable coating composition asclaimed in claim 1 or 2 but having no chromate conversion film.
 17. Analuminum alloy having thereon a coat film formed with a curable coatingcomposition as claimed in claim 1 or
 2. 18. An aluminum alloy havingthereon a coat film comprising a curable coating composition as claimedin claim 1 or 2 but having no chromate conversion film.
 19. A plasticmolded article having thereon a coat film formed with a curable coatingcomposition as claimed in claim 1 or 2.